Board & Card Games Stack Exchange is a question and answer site for people who like playing board games, designing board games or modifying the rules of existing board games. It's 100% free, no registration required.

Put three 1/1 red Human creature tokens with haste onto the battlefield. Sacrifice those tokens at the beginning of the next end step.

The sacrifice portion is not important to this question. What is important is how these two cards interact with eachother.

Playing this card in my first main phase, assuming no counters or other shenanigans by my opponent, I will have my Commander and 3 tokens on the battlefield. What will happen in terms of the power/toughness of my tokens and Commander?

Option A

The tokens will each be 1/1. They don't see each other come in at all. The Commander is 3/3, as one "Enter the Battlefield" trigger happens.

Option B

The tokens will be 1/1. They don't see each other come in at all, because they weren't on the battlefield to see any of the triggers. The Commander is 5/5, as he saw three "Enter the Battlefield" triggers occur.

Option C

The tokens will all be different, with one being 3/3 as he saw the other two come in, one being 2/2 as he saw only the last one come in, and 1/1 as the last one saw none come in.

Option D

The tokens will all be 4/4, as three creatures entered the battlefield this turn.

I am obviously hoping for this option. It may be supported by a ruling on Goldnight Commander that says, emphasis mine,

The creature that entered the battlefield will also get +1/+1 until end of turn if it's still on the battlefield when the ability resolves.

The key being the ability resolving. So my thought is thus:

Thatcher Revolt goes on the stack.

Thatcher Revolt resolves, and three seperate "enter the battlefield" triggers go on the stack as the three humans enter the battlefield as 1/1.

The last (it is a stack) "etb" trigger resolves. This puts an ability from Goldnight Commander on the stack. This resolves and the humans are now all 2/2.

The next "etb" trigger resolves. This puts a new ability from Commander on the stack, and resolves with the humans being 3/3.

The first "etb" trigger finally resolves, puts a Command ability on the stack, which resolves putting the humans at their final state of 4/4.

Option E

The tokens will all be 2/2.

Thatcher Revolt goes on the stack.

Thatcher Revolt resolves, and one single "enter the battlefield" trigger goes on the stack.

The "etb" trigger resolves. This puts an ability from Goldnight Commander on the stack. This resolves and the humans are now all 2/2.

I would really like to have a complete understand both of the result and how that result is calculated by the game engine.

As a player is about to receive priority, you place Goldnight Commander's ability on the stack three times. [CR 603.3]

The third instance of Goldnight Commander's ability resolves: Creatures you control get +1/+1 until end of turn.

The second instance of Goldnight Commander's ability resolves: Creatures you control get +1/+1 until end of turn.

The first instance of Goldnight Commander's ability resolves: Creatures you control get +1/+1 until end of turn.

Three continuous effects were created by a triggered ability. They will only affect the creatures that existed when the abilities resolved [CR 611.2c], but all three of the 1/1s were on the battlefield when they resolved.

So all three of your 1/1 are now 4/4 until end of turn (and your Commander is 5/5 until end of turn).

* — To answer your title question, yes. If you had two creatures with a triggered ability such as "When another creature enters the battlefield, ...", they would see each other entering the battlefield. This is codified by CR 603.6d: "Normally, objects that exist immediately after an event are checked to see if the event matched any trigger conditions. [...]"

For example, if two Goldnight Commander entered the battlefield simultaneously, both of their abilities would trigger [CR 603.6d], and both would end up getting +2/+2 until end of turn.